1. Field of the Invention
The present invention relates to a system and method for improved viewing and navigation of large digital images, such as whole slide images used in microscopy. More particularly, the present invention relates to a system and method that displays the digital image along with movable navigation and field of view boxes that enable a viewer to pan the digital image in an accurate manner, and also performs automatic absolute reorientation of the digital image and the automatic relative reorientation of subsequent digital images in relation to the first digital image.
2. Description of the Related Art
Static images produced by microscope mounted cameras and robotic telepathology systems have been used for many years for clinical telepathology, largely for frozen section and other consultation. It is widely accepted that the images produced by these systems provide sufficient information for their intended purposes. While these systems are useful for low volume applications such as frozen sections and consultations, they are generally not practical for high volume usage applications such as primary diagnosis, quality assurance, or diagnostic immunohistochemistry. In addition, whole slide image systems produce a superior image when compared to images produced by static image systems. Whole slide images are captured with greater resolution, wider dynamic range, and often higher color fidelity.
As understood in the art, when using a microscope to view a slide image, the user (e.g., a pathologist) scans the slide of tissue at low magnification (e.g., 5× magnification) by slowly passing each portion of tissue underneath the lens. At this magnification, a small piece of tissue can result in, for example, 10 to 100 ‘fields of view’ that need to be screened for abnormalities. When an area of interest is identified, the pathologist quickly switches to medium magnification (e.g., 10× magnification) to more closely examine the focus. Again, the pathologist slowly scans this now magnified area in the same manner, and if further resolution is required, the pathologist switches to a higher magnification objective (e.g., 20× magnification) for visualization of even further detail. The most important behavior to note is that the use of ‘smooth, slow panning’ to screen the slide is central to workflow, as a typical pathologist screens hundreds of glass slides per day.
The visual information contained in whole slide images is typically sufficient for pathologists to make reliable diagnoses from whole slide images alone. Recent targeted validation studies have concluded that whole slide images can be used in place of glass slides. As is understood in the art, large images, such as whole slide images in pathology, are difficult to navigate and scan when the image is significantly larger than the field of view that can be represented on a single screen. Large images are especially difficult to navigate over remote distances, that is, when the data is stored at one location and accessed at another location. Since it is generally impractical to wait for the transfer of the entire image file before the user can view the image, selected regions of interest are delivered on demand as a stream of data into the field of view.
Current viewing instruments attempt to provide smooth, slow panning by using either of two methods. The first is the click and drag method in which a mouse cursor typically is in the shape of a hand and navigation occurs by clicking and dragging in a ratcheting manner. This results in hundreds of large hand movements per slide and is impractical for large volume work. The second method employs a thumbnail navigator whereby the mouse cursor is a box-shaped reticle on a low resolution thumbnail image of the entire slide which represents the current field of view. The low resolution thumbnail image is static, and the ‘field of view’ is dynamic. Moving the reticle moves the corresponding field of view. This method can be generally well-suited for low objectives. However, as the magnification increases, the reticle size is reduced, and the sensitivity of movements is increased. That is, the same hand movement that provided a smooth slow pan at low power results in a jerky, difficult to control movement at high power. Hence, users typically compromise by using the thumbnail navigator method at low power and the click and drag method at high power. However, this compromise is very insufficient for high volume work.
In addition, anatomic pathologists typically examine several hundred glass slides per day during clinical practice. Specimens can be subdivided into classes based on their organ system, and subspecialties in pathology typically focus on a particular organ system. Pathologists typically apply their diagnostic algorithms in a routine workflow behavior (e.g. top-down, left-right) and the glass slides are delivered to the pathologist in a consistent orientation. However, it is impractical to perfectly orient the tissue on each instance of a glass slide, thus the pathologist manually orients the glass slide underneath the microscope lens.
Anatomic pathologists also typically examine several ‘slices’ of a tissue biopsy. When a biopsy is processed, it is typically fixed and embedded into a paraffin block, which is mounted on a microtome where a histotechnologist shaves thin slices of the paraffin and tissue and places representative slices onto a glass slide. These glass slides are then stained and delivered to a pathologist, who examines them under a microscope for pathology. During the process of fixation and embedding, a fragment of a tissue biopsy assumes a unique shape. For example, a cylindrical core biopsy from prostate tissue can curl into an ‘S’ shape. 3-dimensional structures (such as glands or tumors) may be partially present in the first slice, and become more apparent in subsequent slices. When a suspicious lesion is identified in one slice of tissue, corresponding foci of tissue in the adjacent slices must be identified and examined for similar pathology. In many types of biopsies, an absolute orientation cannot be deduced. To identify corresponding foci of tissue amongst multiple slices on separate glass slides, the pathologist manually matches the foci of tissue. That is, if a lesion lies at the tip of the ‘S’ shape, the pathologist identifies the same ‘S’ tip on the adjacent slices of tissue, keeping in mind that the tissue slice is likely not in the exact same orientation as the first slice (unlike a CT scan in radiology). Furthermore, special stains are often performed to help further identify suspicious lesions on glass slides. These special stains are performed on adjacent slices of tissue, and in these cases matching specific foci of tissue is also critical.
Currently, there does not exist a method to navigate and orient a digital slide as efficiently as one can with a glass slide.